1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus and a computer program product.
2. Description of the Related Art
Conventionally, an ultrasonic diagnostic apparatus has advantages, such as simple and easy operability and noninvasiveness without risk of radiation exposure, compared with other medical image diagnostic apparatuses, for example, an X-ray diagnostic apparatus and an X-ray Computed Tomography (CT) apparatus; and is used in a medical practice of today for an examination or a diagnosis of the condition of a tissue among various living body tissues, for example, a heart, a liver, a kidney, a mammary gland, or a muscle.
An ultrasonic diagnostic apparatus transmits an ultrasonic wave from an ultrasonic probe in contact with a body surface of a subject, and receives an ultrasonic wave reflected from an internal tissue of the subject, thereby creating an ultrasound image. A general ultrasonic diagnostic apparatus creates a tomogram (two-dimensional image) of a tissue inside the subject by scanning a certain cross section with an ultrasonic wave, by using a one-dimensional ultrasonic probe in which a plurality of ultrasonic transducers is arranged in one row in the scanning direction.
Moreover, recently, an ultrasonic diagnostic apparatus has come into practical use, which creates a three-dimensional ultrasound image (volume data) substantially in real time by using a mechanical scan probe that performs a two-dimensional scan with an ultrasonic wave by mechanically sliding a one-dimensional ultrasonic probe, or by using a two-dimensional ultrasonic probe that performs a two-dimensional scan with ultrasonic waves from a plurality of ultrasonic transducers arranged in a matrix (for example, see JP-A 2000-13266 (KOKAI)).
For a diagnosis by using an ultrasonic diagnostic apparatus, a realtime responsiveness of an ultrasound image created by the ultrasonic diagnostic apparatus is required as well as improvement in the image quality of the ultrasound image created by the ultrasonic diagnostic apparatus.
Parameters for improving the image quality of an ultrasound image includes focus processing by delay control of a transmitting-receiving system, filtering processing by echo filter, sensitivity improvement processing by improving reception dynamic range, signal processing on reception data, and processing for improving a spatial resolution in an lateral direction, which is particularly required among them.
To improve a spatial resolution in the lateral direction, an increase in the scanning density of ultrasonic waves transmitted from the ultrasonic probe is basically required. When the scanning density is increased, the number of scan lines per unit area or unit volume is increased. Even when creating an ultrasound image focused on the same depth, a required scan time with an ultrasonic wave is increased proportionally to the number of scan lines. Therefore, if scanning density is increased to improve the image quality of an ultrasound image, a scan rate that is the number of scan lines per unit time is decreased, so that realtime responsiveness is lost.
Moreover, a technology of ensuring realtime responsiveness has been known by widening the cover area of each ultrasonic wave to be transmitted from an ultrasonic probe, and reducing a scan time through parallel simultaneous reception of acquiring reception data of different scan lines in one-time of a transmission. In such case, the image quality of a created ultrasound image is lower than that in a case of acquiring reception data of one scan line in one-time of a transmission. Therefore, to achieve both of image-quality improvement and realtime responsiveness of an ultrasound image in a diagnosis by using an ultrasonic diagnostic apparatus, it is required to narrow a scan region of an ultrasonic wave as much as possible.
For this reason, a conventional ultrasonic diagnostic apparatus includes a function of determining a scan region of an ultrasonic wave in advance by referring to an ultrasound image so as to include a region of interest of a diagnosis subject in the ultrasound image. In this way, a scan for an ultrasound image is performed after a scan region is determined, and then an ultrasound image corresponding to the fixed scan region is displayed on a monitor included in the ultrasonic diagnostic apparatus.
According to the conventional technology described above, when the region of interest moves, there is a problem that a stress on a subject and a burden on an operator tend to be large in order to achieve both image-quality improvement and realtime responsiveness of an ultrasound image.
In other words, when an organ itself that is the diagnosis subject cyclically moves due to a breath, a region of interest inside the organ also cyclically moves simultaneously. Because of such motion, to include a region of interest that cyclically moves due a breath surely in an ultrasound image, a scan region of an ultrasonic wave needs to be widened.
When performing a diagnosis on a liver in an abdomen region, because the liver itself to be a diagnosis subject is large, a scan region of an ultrasonic wave is required to be wide, and furthermore, the image quality of an ultrasound image is required to be improved because change in tissue characterization of a tissue inside the liver is influential information as a diagnostic reference. A liver itself cyclically moves due to a breath, so that a scan region of an ultrasonic wave is required to be further widened to ensure that an ultrasound image includes, for example, a tumor inside the liver as a region of interest.
In this way, when a region of interest moves, a scan region is widened to ensure that the region of interest is to be included in an ultrasound image as well as to improve the image quality, the number of scan lines tends to increase, as a result, realtime responsiveness tends to be lost.
To secure realtime responsiveness, a doctor or an engineer who is an operator of the ultrasonic diagnostic apparatus needs to narrow a scan region of an ultrasonic wave as much as possible as described above. For this reason, the operator needs to ask a subject to hold the subject's breath while acquiring an ultrasound image such that an organ itself does not cyclically move due to a breath.
However, “to hold the breath” is not generally easy for a subject, and it is a difficult action particularly for a subject who has a respiratory disease or a subject of a relatively high age. When another scan is repeated because an ultrasound image did not include a region of interest, a subject is required “to hold the breath” more times.
Consequently, in order to avoid stress on the subject, the operator has to continue manually operating the ultrasonic probe in accordance with the breath of the subject for the region of interest to be included in the ultrasound image; however, when creating a tomogram by using a one-dimensional ultrasonic probe, it is not an easy operation to continue adjusting the position of the one-dimensional ultrasonic probe for a moving region of interest to be included in the tomogram, thereby increasing a burden on the operator.
On the other hand, when creating a three-dimensional ultrasound image by using a mechanical scan probe or a two-dimensional ultrasonic probe, a scan region is to be wider than that when creating a tomogram. For this reason, to ensure the image quality (the spatial resolution in an lateral direction) of an ultrasound image and the realtime responsiveness both of which are equivalent to those when creating a tomogram, a scan region of an ultrasonic wave needs to be narrowed.
When creating a three-dimensional ultrasound image, a necessity for the subject “to hold the breath” not to move the region of interest turns more serious than when creating a tomogram; consequently, to avoid stress on the subject, the operator needs to continue manually operating a mechanical scan probe or a two-dimensional ultrasonic probe in accordance with the breath of the subject, similarly to when creating a tomogram.
In such case, ultrasonic waves are two-dimensionally transmitted, so that it is possibly easier to adjust the position of the ultrasonic probe for the region of interest to be constantly included in an ultrasound image than a case of creating a tomogram (two-dimensional image); however, it does not reduce a burden on the operator. Moreover, even though the position of the ultrasonic probe is adjusted, it cannot be ensured that a moving region of interest is to be constantly included in a three-dimensional ultrasound image, consequently, the subject sometimes needs “to hold the breath” in some cases in order to avoid repeating a scan.
Furthermore, generally, a created three-dimensional ultrasound image is scarcely used as it is, and the operator cuts out a cross section that includes the region of interest from a three-dimensional ultrasound image, and then performs a diagnosis by referring to the cut out cross section; therefore, when performing a diagnosis by creating a three-dimensional ultrasound image, a burden on the operator becomes large.